Compressor cylinder unloader



June 30, 1970 c, DEGROFF ETTAL 3,518,032

COMPRESSOR CYL INDER UNLOADER Filed May 24. 1968 INVENTORS:

RICHARD 0. De GROFF THOMAS L. KING flaw 1 1%,

United States Patent US. Cl. 417-440 8 Claims ABSTRACT OF THE DISCLOSUREAn unloader assembly for a gas compressor cylinder includes anopen-throated suction valve and a sleeve having one end abutting thevalve and communicating with the valve throat. The sleeve defines achamber for a reciprocating control piston, and has a port whichcommunicates with the suction chamber of the compressor cylinder. In theunloaded position, the piston uncovers the port to provide a flow pathbetween the suction chamber and the cylinder compression chamber throughthe valve throat; and in the loaded position the control piston coversthe sleeve port to close this flow path. The control piston is vented toequalize the pressure acting across it, and is shifted between theloaded and unloaded positions by a fluid operated actuator piston.

BACKGROUND OF THE INVENTION In gas compressors having a well known typeof suction valve assembly which includes a seat member, a stop platemember, and valve closures in the form of disks,

rings, or reeds which are normally urged against associated seats on theseat member, it is conventional practice to unload the compressorcylinder by mechanically lifting and holding the valve closures offtheir associated seats. This is usually accomplished by a reciprocablemember having fingers which extend through the air passages in the valveseat member to engage the closures. This type of unloader mechanismoperates very effectively at low differential pressures;however, atpressure differentials of 500 p.s.i. and above, this type of unloadermechanism is not so effective. At the higher pressures, the valveassembly may become overheated due to the relatively low orificecoeflicient, the force necessary to unseat the valve closures from theirvalve seats may become excessive, and the valve closures may becomedamaged because of the high impact forces of the valve closures on theseats at the time of loading. Excessive temperature is aparticularproblem at higher differential pressures, due to therestricted and tortuous flow paths through valves of this type; and thiscondition is aggravated by the fingers of the unloader mehanism whichnecessarily extend through the valve passages and further restrict airflow during both the loaded and unloaded conditions.

An object of the present invention is to provide an improved unloaderassembly for a compressor cylinder which is particularly effective athigher differential pressures, and which requires minimum force foroperation.

SUMMARY OF THE INVENTION An unloader assembly according to the inventionincludes a conventional suction valve which is provided with a centralpassage or throat. A tubular member engaging the outboard face of thevalve communicates with the valve throat, and includes a wall port whichcommunicates with the cylinder suction chamber. A control piston,slidable within the tubular member, closes communication between thevalve throat and the port in one position and opens communicationbetween the valve passage and port in another position.

3,518,032 Patented June 30, 1970 ice BRIEF DESCRIPTIOIN OF THE DRAWINGaxially through a suction valve and unloader assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing there is shown afragmentary portion of a compressor cylinder including an inner wallportion 11 which defines a wall 12 of the compressor chamber, and anouter wall portion 13 which defines an exterior wall. A cylinder suctionchamber 14 is defined between the walls 11 and 13.

A suction valve opening 15 is provided in the inner wall 11communicating the suction chamber 14 and the compression chamber; andthis opening 15 is provided with an outward facing shoulder 16 whichaccommodates the suction valve 18. The outer wall 13 includes a largeropening 17, aligned with the valve opening 15.

The suction valve 18 is of conventional design, consisting of a stopplate member 19 and a seat member 20 defining a valve lift chamber 21,and a pair of concentric valve closure rings 22 urged against theirrespective valve seats by springs 23. Radially and angularly spacedtransverse passages 24 in the valve seat member communicate the valvelift chamber 21 with the suction chamben 14; and radially and anguarlyspaced transverse passages 25 in the stop plate member communicate thevalve lift chamber 21 with the compression chamber. On the suctionstroke, then, the closure rings 22 are unseated, and the gas flows intothe compression chamber through the passages 24 past the closures 22,then through the passages 25. On the compression stroke, of course, theclosure rings 22 seat against the valve seats preventing flow throughthe valve in the reverse direction.

The valve 18 is seated on the shoulder 16, and sealed relative theretowith a suitable gasket; and the valve is provided with a transversecentral passage or throat 26 which provides an alternative flow paththrough the valve between the suction chamber 14 and the compressionchamber. The outer face of the valve defined by the seat member 20includes an inner peripheral shoulder 27, adjacent the throat 26, and anouter peripheral shoulder 28.

The suction valve 18 is secured against the cylinder shoulder 16 by avalve chair 29 consisting of a flange portion 30 and an integraldownwardly extending sleeve portion 31. The sleeve portion 31 extendsthrough the opening 17 in the outer cylinder wall 13; and the lower endof the sleeve portion 31 seats on the valve shoulder 28. The valve chairis secured to the cylinder wall .13 by means of suitable bolts 33 whichpass through openings in the flange portion 30. The sleeve portionprovides a close fit with the cylinder wall opening 17, and is sealedrelative thereto by a suitable O-ring received in an annular groove inthe sleeve portion.

The valve chair flange portion 30 is provided with a central opening 35which is aligned with the throat 26 of the valve 18. The opening 35accommodates tubular sleeve 38, the lower end of which seats on theinner valve shoulder 27 and is sealed to the valve by means of a of asuitable gasket. The upper end of the sleeve 38 provides a close fitwith the opening 35, and is provided with an externalannular grooveaccommodating a suitable O-ring to provide a seal between the sleeve andopening.

The sleeve 38 defines a cylindrical chamber 40 for an elongatedcylindrical control piston 41; and is provided with one or more wallports 42 which communicate the interior and exterior of the sleeve. Thepiston 41 has an axial length greater than the axial span of the ports42;

and is provided with piston rings 43 adjacent its ends for the purposeof providing a seal between the piston and sleeve both above and belowthe ports 42, when the piston is in the position as illustrated in solidlines in the drawing. This is the loaded position of the control piston41, wherein the piston 41 closes ofl? communication between the valvethroat 26 and the sleeve ports 42. The valve chair sleeve portion 31 isalso provided with one or more ports 44, so that the sleeve ports 42 arecontinuously communicated with the cylinder suction chamber 14.

The control piston 41 is actuated by a fluid operated actuator 48including a generally cylindrical housing defined by a cup-shaped body49 and a cover 50. The bottom wall of the body 49 includes a downwardlyextending cylindrical boss 51 which is received with a close fit withinthe valve chair opening 35, and is sealed relative to the opening bymeans of an O-ring received in an external annual groove in the boss 51.The actuator 48 is secured to the valve chair flange portion by means ofstuds 53, which pass through the actuator body 49 and cover 50', andassociated nuts. The actuator 48, then, secures the sleeve 38 againstthe valve shoulder 27 and closes the upper end of the sleeve.

The actuator body and cover define a closed cylinder chamber 56 for anactuator piston 57 which reciprocates within the chamber in sealedrelation with the chamber walls. The actuator piston 57 and the controlpiston 41 are coupled together in axially spaced relation by means of aspindle 58, the spindle passing through a bore 59 in the actuator bodyboss 51 and being sealed relative thereto by a suitable O-ring. Thespindle 58 is provided with an outer extension 61 which passes through asuitable bore 6-2 in the actuator cover 50 in sealed relation therewith.

Suitable passages 65 and 66 are provided in the actuator housing fordirecting operating fluid to and from the chamber 56, respectively aboveand below the actuator piston 57, for the purpose of shifting theassembly of the pistons 57 and 41 between upper and lower positions. Inthe drawing the piston assembly is shown, in solid lines, in the lowerposition, in which the unloader assembly is in the loaded condition. Thepiston assembly is shifted to and maintained in this position by fluidunder pressure directed to the chamber 56 through the passage 65. Inthis position, the control piston 41 spans the sleeve ports 42; and thepiston rings 43 provide seals between the piston and sleeve both aboveand below the ports 42. The control piston 41 is provided with one ormore vent passages 45 which provide communication between the oppositefaces of the piston and serve to equalize the pressures acting on theopposite faces. With this arrangement, it is not necessary to overcomethe compression chamber pressure in order to shift the control piston 41to the loaded position. With the unloader assembly in the loadedcondition, the suction valve 18 functions in the usual manner to admitgas to the compression chamber.

In order to shift the piston assembly to the upper position, in whichthe unloader assembly is in the unloaded condition, fluid under pressureis directed to the chamber 56 through the passage 66, while the chamber56 above the actuator piston 57 is vented. The piston assembly thenmoves to an upper limiting position which is defined by a stop sleeve 52secured to the actuator cover 50. This stop sleeve 52 limits the upwardmovement of the piston assembly to a position where the sleeve port 42is completely uncovered. Full communication is then provided between thecylinder suction chamber 14 and the cylinder compression chamber throughthe valve chair port 44, the sleeve port 42, the sleeve 38, and thevalve throat 27.

The stop sleeve 52 also serves as a positioning boss for one or morecompression springs 67, which serve to urge the piston assembly to thelower or loaded position.

The spindle extension 61 serves as an external visual indicating for theposition of the control piston 41.

Because the above-described unloader assembly employs an open-throatedsuction valve, the orifice coefficient of the unloaded valve is verygreatly improved. This provides the advantages that the valve operatesmuch cooler during the unloaded condition and that less enginehorsepower is required during the unloaded condition because there isless restriction to the flow of air into and out of the cylindercompression chamber. Also, the orifice coefiicient of the suction valveis improved during the loaded condition because of the absence ofunloader fingers in the valve passages. Because of the design whereinthe pressures are balanced on the opposite sides of the control piston,the forces necessary to move the mechanism to either the loaded orunloaded position are only those necessary to overcome the sealfriction. The mechanism, therefore, is particularly well adapted foroperation with cylinders at higher differential pressures; and permitsthe design of an unloader mechanism for compressor units where it wasnot heretofore feasible.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a gas compressor having a compressor cylinder, a compressor pistonslidable in said cylinder, a suction chamber, and a suction valvecommunicating said suction chamber and said cylinder: an unloaderassembly for said cylinder comprising:

a tubular member engaging the outboard side of said suction valve; saidsuction valve being open-throated to define an air passage therethroughcommunicating with said tubular member; said tubular member having awall opening defining a port communicating with said suction chamber;

a control piston slidable in said tubular member; said control pistoncutting off communication between said port and said air passage in afirst position, and opening communication between said port and said airpassage in a second position; and means for moving said control pistonbetween said first and second positions.

2. The assembly set forth in claim 1:

means closing the outboard end of said tubular member; said controlpiston having a longitudinal extent greater than that of said port, andsaid piston covering said port in said first position; and

passage means extending between the opposite faces of said controlpiston to equalize the pressures acting thereon.

3. The assembly set forth in claim 1:

an actuator for said control piston including housing defining a closurewall for the outboard end of said tubular member; an actuator pistonslidable within said actuator housing; spindle means coupling saidcontrol piston and said actuator piston, said spindle means extendingthrough said closure wall in sealed relation therewith; and means fordirecting an actuating fluid to the opposite faces of said actuatorpiston.

4. The assembly set forth in claim 3:

V an indicator rod extending outwardly from said actuator piston inparallel relation to said spindle; said indicator rod extending throughthe outboard wall of said actuator housing to visually indicate theposition of said control piston within said tubular member.

5. The assembly set forth in claim 3:

spring means in said actuator housing engaging said actuator piston tourge said control piston to said first position.

6. The assembly set forth in claim 1:

said cylinder defining an outward facing shoulder for receiving saidsuction valve; the outboard face of said suction valve defining anoutward facing peripheral shoulder; a valve chair engaging said valveshoulder; means securing said valve chair to said cylinder,

whereby said valve is retained against said cylinder shoulder;

said valve chair defining a wall opening axially aligned with said valvepassage and axially spaced therefrom; and said tubular member engagingsaid suction valve in sealed relation at its inboard end and engagingsaid valve chair wall opening in sealed relation at its chair; saidactuator housing engaging the outboard end of said tubular member tomaintain said member in engagement with said valve.

References Cited outboard end.

7. The assembly set forth in claim 6: an actuator housing defining anoutboard closure wall for said tubular member;

said actuator housing defining an actuator cylinder;

an actuator piston slidable in said actuator cylinder; a spindlecoupling said actuator piston and said control piston, said spindlepassing through said closure wall in sealed relation; and means fordirecting an actuating fluid to the opposite faces of said actuatorpiston to shift said control piston between said first and secondpositions.

8. The assembly set forth in claim 7: means for securing said actuatorhousing to said valve UNITED STATES PATENTS 770,784 9/1904 Steedman230--30 1,291,854 1/1919 Haight 23030 X 1,948,907 2/1934 Egli 23028 102,751,143 6/1956 Biehn 230*24 2,831,625 4/1958 Hartwell et a1 230243,076,593 2/1963 Newton 23022 X 3,294,314 12/1966 Ott et a1. 23024 15WILLIAM L. FREEH, Primary Examiner WARREN J. KRAUSS, Assistant ExaminerU.S. Cl. X.R.

